Method for the purification of iron and steel



Patented Aug. 11, 1931 um'rao STATESJPATENI orrlca m JAEGER, OF IBITTERFELD, ERNST POK ORN Y, OF LEIPZIG, AND GOTTHARD GOSS- RAU, OF IBITTERFELD, GERMANY, ASSIGNORS TO I. G. FAR-BENINDUSTRIE AKTIEN- GESELLSCHAI'T, OI FRANKFORT-ON-THE-MAIN, GERMANY, A CORPORATION OF GERMANY METHOD ron rm. unirrca'rron or moiv AND scram.

No Drawing. Application filed December 13, 1928, Serial No. 325,906, and in Germany December 17, 1927.

This invention relates to the treatment of iron and steel in the molten state with cerium. The use of cerium for the purificationof the molten metal is an established practice 5 in iron and steel foundry-work. The peculiar effect exercised by the addition of cerium consists in the fact that the latter reacts with certain impurities generally contained in the melt such as oxygen, sulphur, nltrogen or phosphorus, forming non-metall1c compounds, which are then eliminated in the form of slag. Owing to its strong tendency to react with the said impurities, cerium should be enerally preferred to other means 1 1 tried for t e same purpose; however the application of cerium produces a slag havmg a high melting-point'and a high viscoslty, both rendering the separation of the slag from the molten metal extremely diflicult and thus constituting a drawback of the process which can be but imperfectly eliminated by overheatin the metal, the latter procedure being limite by technical considerations.

We have now discovered that the separation of the reaction-products of cerium from the melt may be considerabl facilitated in a simple manner by lowering t e melting-point and thereb simultaneously reducing the viscosity of these reaction-products, this being effected by adding the cerium to the bath, not in the elemental form or as a cerium-iron alloy alone, but in combination with other suitable elements actin in a similar though less vigorous way, i. e., ikewise forming nonmetallic reaction-products with the impurities dissolved in the melt. We have found that vanadium, titanium, calcium, aluminium and silicon are suitable for this purpose, although we do not wish to limitourselves to these substances.

Sometimes it is found desirable to incorporate small amounts of, e. g.-, vanadium or titanium, as an alloying metal into the iron. Heretofore, a large percentage of these valuable additional constituents was absorbed by their reaction with the impurities contained in the bath; they were thus partly converted into slag and their effect as alloying sub- 50 stances was hereby diminished to a large degree. By applying these elements simultaneously with cerium, a furthemadvantage of our invention is experienced. Owing to the greater chemical aifinity ofcerium, the greater part of the impurities contained in the bath is absorbed by the cerium present; only a comparatively small amount of the alloying metal is in this case consumed by the reaction, hereby lowering the melting point of the cerium-compounds formed, whilst the main part of the alloying substance does not partake in the reaction, but is left to exercise its effect as an alloying constituent of the iron.. By this method, it is, at the same time, possible to limit more accurately the amount of the alloying metal contained in the iron after the process of purification is accomplished.

Following this method, alloys of to percent of vanadium and 2 to 40 percent of cerium, the remainder being iron, have proved particularly satisfactory when added in suitable proportions to the melt. The quantity of the alloy to be added to the melt and the preferable ratio between its vanadium and cerium contents are determined by the desired vanadium contents of the melt on the one hand and the amount of oxides and like impurities contained in the untreated melt on the other hand, the latter item being generally known from experience. For example, about one to two percent of an iron alloy containing about 30 percent of vanadium and 3 percent of cerium are added to an iron melt containing in addition 0.6 percent Mn the following impurities: 0.5 percent Si, 0.06 percent P, 0.05 percent S, 0.02 percent N, 0.02 percent 0. In this case, the losses otherwise incurred by the formation of oxdyic and other vanadium-compounds are reduced to quite a small extent, the main quantity of the vanadium added being left in the IIOD. as an alloying constituent.

In all cases, where cerium is mentioned in the foregoing specification of our invention and in our claims, it is understood that mischmetal is included by this expression.

We claim:

1. The improvement of the method for state by the addition of cerium, consisting in lowering the melting-point of the cerium-reaction-products by adding vanadium together with cerium, thereby forming a slag, and separating the slag from the molten metal.

2. The improvement of the method for the purification of iron and steel in the molten state by the addition of cerium, consisting in lowering the melting-point of the cerium-reaction-products by adding vanadium together with cerium in the form of an alloy, thereby forming a slag, and separating the slag from the molten metal.

3. The method for the purification of iron and steel in the molten state, which consists in adding an alloy of from 25 to 40 percent of vanadium and 2 to 40 percent of cerium, the remainder being iron, to the bath, thereby forming a slag, and separating the slag from the molten metal.

4. The improvement of the method for the purification of iron and steel in the molten state by the addition of cerium, consisting in lowering the melting-point of the cerium reaction products by adding at least one metal of the group consisting of vanadium, titanium, and aluminium together with cerium, thereby forming a slag and separating the slag from the molten metal.

In testimony whereof we have hereunto set our hands.

MAX J AEGER. ERNST POKORNY. GQTTHARD GOSSRAU. 

